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Inspection apparatus and method for producing image for inspection

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Inspection apparatus and method for producing image for inspection


In order to obtain a quality image without deterioration owing to radiation noise in inspection using the optical video camera in high radiation environment, an inspection apparatus is formed of an image pick-up unit, an image obtaining unit which fetches a video image that contains a signal (noise) that is substantially independent of each frame obtained by the image pick-up unit, a local alignment unit which locally aligns frames with different time phases for forming the image fetched by the image obtaining unit, a frame synthesizing unit which synthesizes the plurality of frames aligned by the local alignment unit for generating a synthesis frame with an SN ratio higher than the SN ratio of the frame before frame synthesis, and an image output unit for displaying or recording the image formed of the synthesis frame generated by the frame synthesizing unit.
Related Terms: Camera Video Camera Optic Local Alignment Optical Inspect

Browse recent Hitachi-ge Nuclear Energy, Ltd. patents - Hitachi-shi, JP
USPTO Applicaton #: #20140210988 - Class: 348 82 (USPTO) -


Inventors: Kenji Nakahira, Atsushi Miyamoto, Naoki Hosoya, Minoru Yoshida

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The Patent Description & Claims data below is from USPTO Patent Application 20140210988, Inspection apparatus and method for producing image for inspection.

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CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No. 13/160,108, filed on Jun. 14, 2011, which claims priority from Japanese Patent Application No. 2011-016614, filed on Jan. 28, 2011 and Japanese Patent Application No. 2010-170561, filed on Jul. 29, 2010, the disclosures of which are expressly incorporated by reference herein.

BACKGROUND

The present invention relates to an inspection apparatus for inspection using an image picked up by an optical camera, and a method for producing the image for inspection.

The system for handling radiation, for example, power plant has been demanded to ensure high safety, and required to execute sufficient inspection on a regular basis. Structures of the nuclear power reactor, for example, the reactor pressure vessel, the shroud in the vessel, the core support plate and the like are inspected as inspection objects. The inspection for objects other than those of the nuclear power reactor, for example, fuel assembly has been conducted.

The inspection method conducted by visually checking the surface condition of the inspection object using the optical camera has been employed as one of the inspection methods. In the visual checking, the camera is brought to close to the object, and the picked up image is shown on the display provided in a location with less radiation apart from the object so that the inspector performs the visual checking. The picked-up images are recorded so as to be confirmed later. The camera is provided with a remote-control operation function using a drive unit for mobility in the image pick-up area, or structured to allow the inspector to manually operate the camera from the place apart from the image pick-up area. Color or gray scale video information is obtained from the camera.

The inspection is conducted in the environment with high radiation intensity, for example, gamma ray, and noise is likely to be superimposed on the image picked up by the camera under the radiation influence, thus deteriorating visibility. This may cause the problem which hinders establishment of high reliability for inspecting soundness of the object. For this, the structure provided with radiation shield has been disclosed in Japanese Unexamined Patent Publication No. 9-311193 for reducing the influence of radiation on the camera.

The radiation may damage electronic circuit in the camera, and its functions as well. Especially, the recent miniaturized semiconductors tend to be susceptible to the damage. Once it is damaged, the camera element with high resolution, the one with wide dynamic range, and integrated circuit required for transmitting a large amount of image signals at high speeds hardly work. If durability against radiation is prioritized, the camera which employs few electronic circuits needs to be used as the one with low resolution and narrow dynamic range.

Meanwhile, Japanese Unexamined Patent Publication No. 10-221481 discloses the compact inspection device, and inspection device capable of traveling underwater aiming at the inspection in the narrow portion and easy operation.

The method is considered as applicable for reducing radiation noise by subjecting the obtained image to the image processing. Use of smoothing filter and median filter has been known as a general denoising method.

During the normal inspection, the lighting device is brought to be close to the object together with the camera for illumination. If the inspection object has a three-dimensionally complicated structure, the region which allows placement of the camera or the range which allows the illumination to reach are limited, making the illumination partially insufficient or excessive.

So another problem arises that it is difficult to pick up the video image by the camera for inspection under the appropriate illumination.

Japanese Unexamined Patent Publication NO. 2009-271096 discloses the method for executing contrast correction by obtaining correction formula based on brightness in the dark field and the brightness in bright field of the digital camera so as to improve visibility in reference to brightness of the image.

Japanese Unexamined Patent Publication No. 2009-65350 discloses the method for synthesizing a plurality of images each picked up by varying the exposure condition into the image in the digital camera field.

It is difficult for the method as proposed in Japanese Unexamined Patent Publication No. 9-311193 to reduce size and weight of the inspection device because of its radiation shield. In order to reduce the gamma-ray dose to 10%, the thickness of the apparatus needs to be 4 cm or larger while using lead which has been widely used as the gamma-ray shielding material.

Meanwhile, provision of the radiation shield for the device as disclosed in Japanese Unexamined Patent Publication No. 10-221481 is not practical from the aspect of size and weight.

General denoising process using the smoothing filter and median filter may cause problems as below. It is difficult for the smoothing filter and the median filter to appropriately suppress only the radiation noise while storing the component (signal component) except the radiation noise. The smoothing filter tends to deteriorate the high-frequency component of the signal to provide blurred images. The median filter provides substantially quality images when the noise amount is low, but may have its performance deteriorated when the noise amount is increased. When using the space filter with high accuracy such as load median filter besides those described above, improvement of the SN ratio (ratio of amount of signal component to radiation noise amount) is limited.

There is no image processing method for completely removing only noise in any images, and accordingly, deterioration in the signal component and residual noise are unavoidable to a certain degree. As to what degree deterioration in the signal component or the residual noise is allowed may vary depending on the inspection object and inspection type. There exists no interface which allows easy designation of the desired image in reducing the noise through the image processing.

During the actual inspection, there may be often the case that the inspection in wide range is conducted while moving the camera. In such a case, a plurality of positions with different radiation doses have to be inspected, and accordingly, the radiation noise amount contained in the image may vary as the camera moves. Under the environment with a small noise amount, denoising may be conducted relatively easily. However, under the environment with a large noise amount, it is difficult to conduct denoising. Therefore, it is difficult to provide quality image regardless of noise amount.

The method disclosed in Japanese Unexamined Patent Publication No. 2009-271096 applies the same contrast correction over the entire image, which fails to greatly improve visibility of interest region locally.

The method disclosed in Japanese Unexamined Patent Publication No. 2009-65350 requires a plurality of images with varied exposure conditions. However, if the inspection object has a three-dimensionally complicated structure to ensure reliability of inspection, it is difficult to arbitrarily change the exposure condition.

Under the radiation environment, the structure with radiation shield may be considered for reducing the influence of radiation on the camera. Such structure allows the use of high-performance camera which is hardly damaged by the radiation. In this case, it is difficult to reduce size and weight of the inspection apparatus because of the radiation shield. For example, in order to reduce the gamma-ray dose to 10%, the thickness of the structure needs to be 4 cm or larger while using lead which has been widely used as the gamma-ray shielding material. Therefore, it is not practical for conducting the inspection in narrow portion in terms of size and weight.

In the case where inspection is conducted using the image of the inspection object, which has been picked up by the camera, the method for creating the image with resolution higher than the pixel resolution of the camera may be considered. This method is capable of intensifying the resolution, but fails to improve the contrast of the image having the contrast partially lowered owing to insufficient or excessive illumination. The method is not regarded as the solution for the deteriorated visibility from the aforementioned aspect.

SUMMARY

The present invention provides an inspection method which allows use of the image (same image) with good visibility for inspection, and method for creating the inspection image. The present invention further provides the inspection method which allows improvement of local visibility, and method for creating the inspection image.

The present invention further provides an inspection apparatus for inspecting the image (video image) picked up by the optical camera, and the method for creating the inspection image.

(1) According to the invention, the image (video image) is fetched from the optical camera so that a plurality of frames for forming the image each having different time phase are locally aligned, the locally aligned frames are subjected to the frame synthesis to create the frame with SN ratio higher than the ratio of the frame before synthesis, and the image formed of the synthesized frames is displayed or recorded.

The signal components are correlated among a plurality of frames with continuous time phases, while superimposing the radiation noise on the respective frames substantially independently. The appropriate frame synthesis ensures reduction of the radiation noise while having the signal components stored. Displacement of the signal component occurs among frames owing to movement of the camera. Since the inspection object has the three-dimensional structure, the displacement varies depending on the position on the image. The alignment is locally conducted among frames to allow accurate calculation of the displacement for each local region. As a result, the signal component may be appropriately stored in the frame synthesizing process.

(2) According to the present invention, the component value of the obtained color image corresponding to the light receiving method of the color optical camera is calculated so as to provide the denoising level for each of the respective calculated component values.

For example, it may be considered that the image derived from the color optical camera which is formed of light receiving elements of R (red), G (green), and B (blue) (hereinafter referred to as RGB camera) has the radiation noise superimposed on the R, G, and B components for forming the image substantially independently. The use of the RGB camera ensures calculation of three component values of R, G and B of the derived color information for the respective pixels for synthesizing frames with respect to each of the components. This makes it possible to remove the radiation noise more appropriately compared to the case of frame synthesis for calculating the noise removing level in common to those component values.

(3) According to the present invention, both the image fetched from the optical camera and the image formed of the synthesized frames may be simultaneously displayed or recorded.

If the inspector is allowed to observe not only the image having the radiation noise removed but also the image before removing the radiation noise, more information data may be obtained, resulting in improved usability. For example, the inspector is allowed to visually confirm the radiation noise amount more clearly, and to adjust the processing parameters for removing the radiation noise during the inspection easily while observing both images.

(4) According to the present invention, the image is fetched from the optical camera, a plurality of frames with different time phases for forming the image are locally aligned, the aligned plurality of frames are synthesized to create the frame with an SN ratio higher than the SN ratio of the frame before synthesis, and the image formed of the synthesized frame is displayed or recorded. Furthermore, the radiation noise amount contained in the image fetched from the optical camera is measured, and the processing parameters which relate to the alignment, frame synthesis, or image output are changed in accordance with the measured radiation noise amount.

The method for appropriately removing the radiation noise is different depending on the radiation noise amount. If the noise amount is small, the image with excellent quality may be obtained in spite of the process using only a small amount of frames. On the contrary, if the noise amount is large, it is difficult to suppress noise unless a large number of frames are used. In order to conduct high-performance denoising in the case of large noise amount, it is necessary not only to use a large number of frames, but also conduct complicated process. Use of a large number of frames, and the complicated process may cause disadvantage of prolonged processing time. The number of the frames and other processing parameters may be changed in accordance with the radiation noise amount to constantly provide quality images.

(5) According to the present invention, the radiation noise amount is measured using the frame before frame synthesis and the frame after the frame synthesis.

The radiation noise amount may be measured using the image picked up by the camera. When measuring the noise amount, the radiation noise needs to be extracted with accuracy from the image. Such noise may be extracted with relatively higher accuracy without adding complicated process for measuring the radiation noise amount only by subtracting the frame after the frame synthesis from the frame before the frame synthesis.

(6) According to the present invention, among the processing parameters which relate to alignment, frame synthesis or image output, the image display rate or recording rate is changed.

As the radiation noise amount is increased, more computation is required for removing the radiation noise while storing the signal component. The device with limited computation capability has to sacrifice the denoising performance unless the display rate and recording rate are lowered. For the inspector, it is often the case that the image with less noise may be easily inspected in spite of slightly lowered rate compared to the case where the image with higher noise amount is inspected for displaying or recording at a higher rate. Then the display rate or the recording rate may be changed in accordance with the radiation noise amount for processing while maintaining the higher rate in the case of low noise amount, and while emphasizing the image quality in the case of high noise amount.

(7) According to the present invention, the image is fetched from the optical camera, the image with high SN ratio is created by subjecting the fetched image to the radiation noise removing process, and the created image is displayed or recorded. The calibration function is provided for adjusting the processing parameters which relate to the radiation noise removing process, the image display or image recording using the image for calibration prior to the inspection. With the calibration function, the noise superimposed image obtained through pseudo superimposing of the noise on the image for calibration is subjected to the radiation noise removing process. Interface is further provided to adjust the processing parameters based on the image after the radiation noise removing process.

The calibration function allows adjustment of parameters of radiation noise removing process before inspection for obtaining the image visually recognized by the inspector with ease. Compared with the case where the processing parameters need to be adjusted for each inspection, the aforementioned structure provides advantage of reducing the inspection time. The image which contains no radiation noise may be obtained as the image for calibration so as to compare the image after denoising with the image which contains no radiation noise. This makes it possible to correctly confirm as to what extent the signal component has been deteriorated by the denoising process, or denoising performance upon change in the noise amount.

(8) According to the present invention, the image is fetched from the optical camera, the plurality of frames with different time phases for forming the fetched image are locally aligned, the aligned plurality of frames are subjected to the frame synthesis to create the frame with SN ratio higher than the frame before the frame synthesis, and the created image is displayed or recorded. Furthermore, the calibration function is provided for adjusting the processing parameters which relate to the radiation noise removing process, image display or image recording using the image for calibration before inspection. The calibration function subjects the noise superimposed image obtained through pseudo superimposing of the noise on the image for calibration to the radiation noise removing process. The interface is provided to adjust the processing parameters based on the image after the radiation noise removing process.

As described above, after performing the local alignment as the radiation noise removing process, the frame synthesis is conducted to allow reduction of the radiation noise while appropriately storing the signal components. The calibration function for the process allows appropriate adjustment of the processing parameters which relate to the local alignment and frame synthesis, thus making it possible to provide the desired image quality.

(9) According to the present invention, the calibration function adjusts the processing parameters so that the image obtained by subjecting the noise superimposed image to the radiation noise removing process is brought to be close to the image for calibration before superimposing the noise.

Adjustment of the processing parameters allows the inspector to adjust them only when needed, which makes it possible to provide good processing results while alleviating burden on the inspector for such adjustment.

The present invention provides a method for producing an image for inspection which includes the steps of picking up an inside of an inspection object largely influenced by radiation by a camera to obtain an inner image of the inspection object, receiving the picked up image at a place less influenced by the radiation apart from the inspection object, setting an inner interest region of the inspection object from the received image, correcting a contrast of the image in the set interest region, displaying the image subjected to the contrast correction on a screen, and recording the image having the contrast corrected, which is displayed on the screen in a recording unit.

The present invention provides an inspection apparatus which includes an image pick-up unit which picks up an image (video) of inside an inspection object which is largely influenced by radiation to obtain an inner image of the inspection object, an image processing unit which receives the picked up image obtained by the image pick-up unit at a place less influenced by the radiation apart from the inspection object for processing the received image, an output unit which includes a screen on which the image processed by the image processing unit is displayed, and an image storage unit which stores the image displayed on the screen of the output unit. The image processing unit includes an interest region setting unit for setting an interest region inside the inspection object from the received image, and an image contrast correction unit for correcting a contrast of the image in the interest region set by the interest region setting unit. The output unit displays the image having the contrast corrected by the image contrast correction unit on the screen.

According to the present invention, the plurality of frames with different time phases for forming the image are subjected to the local alignment, and those frames are synthesized so as to create the frame with SN ratio higher than that of the frame before the frame synthesis, thus making it possible to effectively remove the radiation noise.

The present invention provides the apparatus for inspecting the inspection object greatly susceptible to the radiation influence, which may be used for inspecting the image with excellent visibility by conducting contrast correction. The apparatus for inspecting the inspection object greatly susceptible to the radiation influence may have its local visibility largely improved by conducting the correction by setting the interest region.

These features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a basic structure of a visual inspection apparatus according to Example 1 of the present invention;

FIG. 2 is a flowchart that represents the process for denoising by executing image processing of the image having the radiation noise superimposed according to Example 1 of the present invention;

FIG. 3A represents a frame image subjected to the radiation noise removing process;

FIG. 3B represents a reference frame image for executing the frame synthesis;

FIG. 3C represents a frame image having the reference frame split into local regions;

FIG. 3D represents a frame image having the reference frame split into different shaped local regions;

FIG. 3E represents a frame image where the local regions of the reference frame are overlapped;

FIG. 3F represents a frame image obtained by performing the region splitting through segmentation so that the local region with similar characteristics of the image signal on the frame are expressed in the same local region;

FIG. 4A represents the method for aligning the local regions by parallel movement;

FIG. 4B represents an example for aligning the local regions by performing parallel movement and enlargement or contraction, and rotation and distortion;

FIG. 5A is a flowchart representing step of executing the frame synthesis by obtaining median between the reference frame and the target frame;

FIG. 5B is a flowchart representing step of executing the frame synthesis by processing weight calculation and weighted average after subjecting the reference frame to exception removing process;

FIG. 5C is a flowchart representing step of executing the frame synthesis using the target frame after the frame synthesis as the reference frame for the subsequent weight calculation process;

FIG. 6A illustrates a three-dimensional space as an example of brightness value when the radiation noise is superimposed on the color image;

FIG. 6B is a table showing frame synthesis weights for the respective points 603, 604 and 606;

FIG. 7A is an explanatory view with respect to a light receiving principle of a RGB camera of 3-CCD type;

FIG. 7B is an explanatory view with respect to the light receiving principle of the RGB camera of single integration type;

FIG. 8A is a flowchart representing a process for synthesizing frames each subjected to the synthesis for output components of the RGB camera;

FIG. 8B is a flowchart representing a process in which the frame synthesis for two components is conducted, which will be further synthesized to create the synthesized frame;

FIG. 9 is a block diagram illustrating a basic structure of the visual inspection apparatus according to Example 2 of the present invention;

FIG. 10 is a flowchart representing the process for denoising by processing the image having the radiation noise superimposed according to Example 2 of the present invention;

FIG. 11A is a graph showing relationship between noise amount and display rate, which represents the method for changing the display rate in accordance with the measured noise amount according to Example 2 of the present invention;

FIG. 11B is a graph showing relationship between noise amount and the number of frames, which represents the method for changing the display rate in accordance with the measured noise amount according to Example 2 of the present invention;

FIG. 12 represents the flow of the process for measuring the noise amount according to Example 2 of the present invention;

FIG. 13 represents the flow of the process for switching the frame synthesizing method as one of methods for changing processing parameters according to Example 2 of the present invention;

FIG. 14A is a flowchart representing the process for automatically executing the denoising performance evaluation according to Example 2 of the present invention;

FIG. 14B is a flowchart representing the process for manually adjusting the processing parameter for denoising according to Example 2 of the present invention;

FIG. 15 represents the flow of the process for creating a deteriorated image from a base image according to Example 2 of the present invention;

FIG. 16 represents the flow of the process for executing the denoising performance evaluation according to Example 2 of the present invention;

FIG. 17 is a front view of a calibration screen displayed upon calibration according to Example 2 of the present invention;

FIG. 18 is a front view of an image shown on the display upon inspection according to Example 2 of the present invention;

FIG. 19 represents an exemplary flow of a sequence for visual inspection according to an embodiment of the present invention;

FIG. 20A is a block diagram illustrating a brief structure of the inspection apparatus according to the embodiment of the present invention;

FIG. 20B is a block diagram illustrating a structure of an image processing unit of the inspection apparatus according to the embodiment of the present invention;

FIG. 21A shows graphs as examples of general contrast correction, specifically, the graph indicating the frequency distribution of brightness of the input image in the presence of deviation, the graph indicating the correction function, and the graph indicating the frequency distribution of brightness of the output image;

FIG. 21B shows graphs as examples of general contrast correction, specifically, the graph indicating the frequency distribution of brightness of the input image in the absence of deviation, the graph indicating the correction function, and the graph indicating the frequency distribution of brightness of the output image;

FIG. 22A shows graph indicating the frequency distribution of brightness of the input image as an example of the contrast correction while enlarging the distribution at a dark side set as an interest region, a graph indicating a correction function, and a graph indicating the frequency distribution of brightness of the output image;

FIG. 22B shows a graph indicating the frequency distribution of brightness of the input image as an example of the contrast correction while enlarging the distribution at the dark side set as the interest region, a graph indicating the correction function, and a graph indicating the frequency distribution of brightness of the output image;

FIG. 23A represents an image of an inspection object split into a plurality of regions according to an embodiment of the present invention;

FIG. 23B is a graph indicating an example of the correction function which varies for each of the plurality of split regions according to the embodiment of the present invention;

FIG. 24A shows a graph indicating a frequency distribution of brightness of an input image as an example of correcting contrast of the image where the frequency distribution of brightness of the input image is concentrated at the center, a graph indicating the correction function, and a graph indicating the frequency distribution of brightness of the output image;

FIG. 24B represents an image of the inspection object in the state where the portion around the center is automatically set to the interest region according to the embodiment of the present invention;

FIG. 24C is a graph indicating an example of the correction function for correcting contrast of the image in the state where the frequency distribution of brightness of the input image is concentrated on the center according to the embodiment of the present invention;



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stats Patent Info
Application #
US 20140210988 A1
Publish Date
07/31/2014
Document #
14227630
File Date
03/27/2014
USPTO Class
348 82
Other USPTO Classes
International Class
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Drawings
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